This invention relates to a method of assembling a multilayer laminate interconnection board.
Until recently, the preferred interconnection scheme used in assembling mainframe computer printed circuit boards was molybdenum conductors buried in a sintered aluminum oxide substrate. More recently, such circuit boards contain copper conductors buried in a glass ceramic substrate.
There are inherent limitations regarding the use of such ceramic substrates in semiconductor packaging. The package must provide a large quantity of low inductance, low capacitance, closely spaced connections to achieve system execution cycle times less than 10 nanoseconds.
In order to overcome these limitations, it will be necessary to form the interconnections in layers with copper or other low resistance metallic wires or conductors and encase the wires in a low dielectric constant material such as polyimide or other organic dielectric material. The wiring layers, in turn, will be assembled onto an auxiliary pin carrier substrate which provides pins for connection into a circuit board for interconnection with other boards in the computer system.
Each functional layer of the laminated structure is fabricated separately and tested before lamination. The functional layer comprises one or more layers of thin film metal conductor lines. The conductor lines are separated from a ground plane sheet of conductive metal by a layer of dielectric material. An advantage of the functional layer is that the conductive signal lines and corresponding ground plane can be fully tested before fabrication into the laminated structure comprising two or more functional layers. The testing and repair of each layer can be done without disturbing or damaging the adjacent layers. In the prior art, in which the individual thin films are fabricated sequentially, the structure is difficult to repair during fabrication without damaging the previously formed films.
One prior art method of assembling a multilayer laminate is discussed in U.S. Pat. No. 3,436,819 in which holes are drilled through multiple printed circuit board layers after lamination of each layer. When assembling more than a single layer, holes are drilled through previously drilled layers to a lower or to the bottom layer. As will become apparent, the present invention obviates the requirement of a multiplicative step of producing and connecting each layer of wiring in a serial sequence to the auxiliary pin carrier substrate.